Network coding enhancements

ABSTRACT

A method performed by a base station is provided. The method includes receiving, at the base station, a signal containing a transmitted first signal including a network coded message and a transmitted second signal including a non-network coded message, where the second signal is transmitted according to at least one transmission parameter. The method further includes receiving, at the base station, the at least one transmission parameter and determining, by the base station, an interference to the transmitted first signal caused by the transmitted second signal, where the interference is determined using the at least one transmission parameter. The method further includes removing the determined interference from the signal to recover the transmitted first signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. §119(e), this application claims the benefit ofU.S. Provisional Application No. 61/297,187 filed on Jan. 21, 2010 andU.S. Provisional Application No. 61/354,673 filed on Jun. 14, 2010,which are all hereby incorporated by reference herein in theirentireties.

FIELD OF THE INVENTION

The present invention relates to telecommunications, and in particular,to wireless communications.

DESCRIPTION OF THE RELATED ART

In a mobile communications network, a mobile station (MS) cancommunicate with a base station (BS) via a relay station (RS).Typically, communication from the MS to the BS takes place over anuplink (UL) channel, and communication from the BS to the MS takes placeover a downlink (DL) channel. In most time-division duplex (TDD) relaycommunication protocols, an MS may transmit a message intended for theBS to an RS in an UL sub-frame. The RS in turn transmits the message tothe BS in an RS UL sub-frame. On the other hand, a BS may transmit amessage intended for the MS to the RS in a DL sub-frame. The RS thentransmits the message to the MS in an RS DL sub-frame.

The above relay scheme is inefficient, because the MS or the BS willhave to schedule each of the uplink or downlink transmissions handled bythe RS in separate sub-frames. The transmission throughput of a networkimplementing such a scheme is limited due to inefficient use ofbandwidth (i.e., separate channels need to be used for UL and DL ofrelayed messages). If network coding is applied at the RS, the bandwidthusage of relay link can be reduced.

However, if the RS is configured to use multiple-user multiple-inputmultiple-output (MU-MIMO) technology to concurrently transmit a networkcoded message to one MS and non-network-coded messages to other MSs,where the messages are transmitted using different precoding vectors toavoid interference between messages that are intended for an MS andmessages that are not intended for an MS, the network coded messagetransmitted by the RS to BS may suffer interference from other messagesthat are concurrently transmitted by the RS to MSs. As such, the networkcoded messages transmitted by the RS may not be properly decoded by theBS.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the invention, a method performedby a base station includes receiving, at the base station, a signalcontaining a transmitted first signal including a network coded messageand a transmitted second signal including a non-network coded message,where the second signal is transmitted according to at least onetransmission parameter. The method further includes receiving, at thebase station, the at least one transmission parameter and determining,by the base station, an interference to the transmitted first signalcaused by the transmitted second signal, where the interference isdetermined using the at least one transmission parameter. The methodfurther includes removing the determined interference from the signal torecover the transmitted first signal.

It is contemplated that the at least one transmission parameter includesat least a packet identifier, a precoding vector, a power allocation ora modulation coding scheme (MCS). It is contemplated that thenon-network coded message is transmitted according to a precodingvector.

It is contemplated that the transmitted first signal and the transmittedsecond signal are transmitted by a relay station. It is furthercontemplated that the relay station transmits according to amultiple-user multiple-input multiple-output (MU-MIMO) transmissionsystem.

It is contemplated that information in the transmitted second signalincludes information previously transmitted by the base station to arelay station transmitting the second signal.

In accordance with one embodiment of the invention, a method performedby a base station includes receiving, at the base station, a signalcontaining a transmitted first signal including a network coded messageand a transmitted second signal including a non-network coded message,where the second signal is transmitted according to at least onetransmission parameter. The method further includes receiving, at thebase station, the at least one transmission parameter and decoding thesignal using the at least one transmission parameter to recover thetransmitted first signal.

It is contemplated that the at least one transmission parameter isreceived from a relay station transmitting the second signal. It isfurther contemplated that the at least one transmission parameter isdetermined by the relay station.

It is contemplated that decoding the signal includes determining, by thebase station, an interference to the transmitted first signal caused bythe transmitted second signal, where the interference is determinedusing the at least one transmission parameter, and removing thedetermined interference from the signal to recover the transmitted firstsignal.

In accordance with one embodiment of the invention, a method performedby a relay station includes transmitting, from the relay station, afirst signal including a network coded message and a second signalincluding a non-network coded message, wherein the first signal and thesecond signal form a third signal, and where the second signal istransmitted according to at least one transmission parameter. The methodfurther includes transmitting, from the relay station, the at least onetransmission parameter, where an interference to the transmitted firstsignal caused by the transmitted second signal is determined using theat least one transmission parameter, and where the determinedinterference is removed from the third signal to recover the transmittedfirst signal.

In accordance with one embodiment of the invention, a method performedby a user equipment (UE) or network equipment (NE) includes receiving,at the UE or NE, a bitmap including at least a first bit that is aresult of an exclusive OR operation between a portion of a first messageand first data which can facilitate determining information that shouldbe network coded with the first message in a future transmission, wherethe UE is either a transmitter or a receiver of the future transmission,where a first receiver for the bitmap is required to receive the firstmessage and has implicit or explicit knowledge of the first data, andwhere a second receiver for the bitmap has implicit or explicitknowledge of the first message and is required to receive the firstdata.

It is contemplated that when the UE is the transmitter of the futuretransmission, the method further includes determining, by the UE, thefirst data from the first bit in the bitmap using the first message, andidentifying, by the UE, the first data associated with the firstmessage, where the first data indicates whether the first receiversuccessfully received the first message. The method further includesgenerating, by the UE, a network coded message including a retransmitteduplink (UL) message and the first message when the first receiver hasnot successfully received the first message, and transmitting thenetwork coded message.

It is contemplated that the first receiver has previously received a ULmessage, and where the first receiver determines the first message fromthe network coded message using the UL message. It is contemplated thatthe first receiver recovers the portion of the first message from thefirst data in the bitmap.

It is contemplated that when the UE is the receiver of the futuretransmission, the method further includes determining, by the UE, anacknowledgment (ACK) channel assignment using the first message, wherethe ACK channel assignment is used to notify a network that the UE hasreceived the first message, and where an acknowledgment or anon-acknowledgement on the ACK channel is indicated using on-off keying.It is contemplated that when the UE is the receiver of the futuretransmission, the method further includes transmitting an ACK signal tothe network according to the ACK channel assignment and receiving, atthe UE, the future transmission including a network coded message, wherethe network coded message includes a second message to the UE and thefirst message.

It is contemplated that the first transmitter has previously transmittedthe first message to the relay station, and where the UE determines thesecond message from the network coded message using the first messagethat was overheard, and where the first receiver determines the firstmessage from the network coded message using the second message which ithas previously transmitted to the relay station.

It is contemplated that the first receiver recovers the portion of thefirst message from the bitmap using data indicating whether a previoustransmission from the first receiver occurred. It is furthercontemplated that the network generates the future transmission based onthe ACK signal received by the network.

It is contemplated that the first receiver is a base station (BS).

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. It is to beunderstood that both the foregoing general description and the followingdetailed description of the present invention are exemplary andexplanatory and are intended to provide further explanation of theinvention as claimed.

These and other embodiments will also become readily apparent to thoseskilled in the art from the following detailed description of theembodiments having reference to the attached figures, the invention notbeing limited to any particular embodiments disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects and features of the present disclosure willbecome more apparent upon consideration of the following description ofembodiments, taken in conjunction with the accompanying drawing figures.

FIGS. 1A and 1B illustrate a network in accordance with one embodimentof the present invention.

FIG. 2 illustrates the failed downlink packets and failed bi-directionalnetwork coded packets in accordance with one embodiment of the presentinvention.

FIG. 3 illustrates an exemplary timeline of type “A” and type “B” ACKsin accordance with one embodiment of the present invention.

FIG. 4 illustrates a type “A” ACK assignment message in accordance withone embodiment of the present invention.

FIG. 5 illustrates a network in which an exemplary type “A” ACK channelassignment is performed in accordance with one embodiment of the presentinvention.

FIG. 6 illustrates a type “B” ACK assignment message in accordance withone embodiment of the present invention.

FIG. 7 illustrates a network in which an exemplary type “B” ACK channelassignment is performed in accordance with one embodiment of the presentinvention.

FIG. 8 illustrates a network in which an exemplary ACK/NAK echo for abi-directional network packet is performed in accordance with oneembodiment of the present invention.

FIG. 9 illustrates a network in which an exemplary ACK/NAK echo for adownlink packet is performed in accordance with one embodiment of thepresent invention.

FIGS. 10A through 10C illustrate a network that uses network codedcontrol information for identifying a downlink receiver that willbenefit from network coding in accordance with one embodiment of thepresent invention.

FIG. 11 illustrates control information in accordance with oneembodiment of the present invention.

FIGS. 12A through 12C illustrate a network that uses network codedcontrol information for ACK channel assignment in accordance with oneembodiment of the present invention.

FIG. 13 illustrates control information in accordance with oneembodiment of the present invention.

FIG. 14 is a flowchart illustrating a method performed by a BS inaccordance with one embodiment of the invention.

FIG. 15 is a flowchart illustrating a method performed by a BS inaccordance with one embodiment of the invention.

FIG. 16 illustrates a block diagram of a user terminal in accordancewith one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description, reference is made to theaccompanying drawing figures which form a part hereof, and which show byway of illustration specific embodiments of the invention. It is to beunderstood by those of ordinary skill in this technological field thatother embodiments may be utilized, and structural, electrical, as wellas procedural changes may be made without departing from the scope ofthe present invention. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or similarparts.

FIG. 1A shows a network 100 in accordance with one embodiment of thepresent invention. For example, the network 100 can be a cellularnetwork configured to use multiple-user multiple-input andmultiple-output (MU-MIMO) radio transmission techniques fortransmissions from a relay station (RS) to mobile stations (MSs). Asshown in FIG. 1A, the network 100 includes MSi 102, MSj 104, RS 106 andbase station (BS) 108.

In the embodiment of FIG. 1A, the MSi 102 and MSj 104 can each be aportable electronic device capable of wireless communications, such as acellular telephone. The RS 106 can include at least two antennas, suchas antennas 114 and 116, and the BS 108 can include at least oneantenna, such as antenna 118.

As shown in FIG. 1B, the RS 106 can be configured to transmit downlinktransmissions from the BS 108 to one or more MSs in the network 100,such as the MSi 102 and the MSj 104. For example, the RS 106 cantransmit a downlink message from the BS 108 to the MSi 102, such as anon-network coded message 112 shown in FIG. 1B. As shown in FIG. 1B, thenon-network coded message 112 can also be received by the BS 108.

The RS 106 can also transmit downlink messages that are network-codedmessages, which serve as bi-directional messages including informationdirected to both the BS 108 and an MS in the network 100, such as theMSj 102 or the MSj 104. For example, the RS 106 can receive an uplinkmessage from the MSj 104 that is intended for the BS 108, and canreceive a downlink message from the BS 108 that is intended for the MSj104. The RS 106 can then generate a single message, that is, a networkcoded message, including both the information in the uplink message tothe BS 108 and the information in the downlink message to the MSj 104.The RS 106 can then transmit the network coded message, such as thenetwork coded message 110 in FIG. 1B, to the MSj 104 and the BS 108.

Therefore, the BS 108 has knowledge of the content in the non-networkcoded message 112 and the content of the downlink message used togenerate the network coded message 110. However, the BS 108 does nothave knowledge of the content in the uplink message used to generate thenetwork coded message 110.

In one embodiment, each of the downlink messages transmitted from the RS106 intended for different MSs in the network 100 are precoded by the RS106. For example, as shown in FIG. 1B, the network coded message 110 canbe precoded with a precoding vector “Px” and the non-network codedmessage 112 can be precoded with a precoding vector “Py.” Ideally, thenon-network coded message 112 precoded with the precoding vector Pyshould cause a negligible amount of interference to the network codedmessage 110 precoded with the precoding vector Px at the MSj 104.However, the non-network coded message 112 precoded with the precodingvector Py may cause a significant amount of interference to the networkcoded message 110 precoded with the precoding vector Px at the BS 108.

The precoding vector Px may not be the most optimal precoding vectorused by the RS 106 for transmissions to BS 108. Since the relay linktypically has a better channel condition than the access link, a set “P”of precoding vectors Pxs may be adequate for enabling the BS 108 toreceive the transmissions from the RS 106 if there is no interferencefrom other precoded transmissions. In one embodiment, the RS 106 onlyperforms network coding on transmissions intended for MSs whoseprecoding vectors are in the set P.

With reference to FIG. 1B, when the network coded message 110 istransmitted by the RS 106, the control channel of the RS 106 alsotransmits information about the non-network coded message 112. Forexample, the information can include one or more transmissionparameters, such as a packet identifier, a precoding vector, amodulation and coding scheme (MCS) and power allocation information. Thepacket identifier associates the non-network coded message 112 to aprevious packet transmitted by the BS 108 and retransmitted by the RS106 to an MS, such as the MSi 102.

The BS 108 caches the previously transmitted packets for both MSs thatare configured to decode network coded messages, such as the MSj 104 inFIG. 1B, and MSs that are not configured to decode network codedmessages, such as the MSi 102 in FIG. 1B.

The BS 108 receives a signal 120 from the RS 106, which includes thenetwork coded message 110 and interference caused by the non-networkcoded message 112. Upon receiving the signal 120, the BS 108 can use theinformation about the non-network coded message 112, such as the packetassociation, the cached packet and the precoding vector of thenon-network coded message 112, to determine the interference to thenetwork coded message 110. The BS 108 can then remove the determinedinterference from the signal 120 to recover the network coded message110. The BS 108 can use the recovered network coded message 110 and thecontent in the downlink message that was used to form the network codedmessage 110 to determine the content in the uplink message in thenetwork coded message 110.

With reference to FIG. 1A, when the RS 106 generates a network codedpacket that includes both an uplink packet from an MS in the network100, such as the MSi 102, and a downlink packet from the BS 108 to adifferent MS in the network 100, such as the MSj 104, the MSj 104 musthave previously received and decoded the uplink packet from the MSi 102in order for the MSj 104 to decode the network coded packet and recoverthe downlink packet.

Consequently, constraints may be placed on the delay of the uplinkpacket, the resources of the uplink control channel on the access link,the battery power of the MSj 104 and the opportunities for overhearingother uplink traffic. Such constraints may result from the fact that theRS 106 must ensure that there is an MS, such as the MSj 104, that hasdecoded the uplink packet from the MSi 102 before selecting one or moredownlink packets to be network coded with the uplink packet from the MSi102. Such constraints may also result from the fact that MSs that are inthe mobile station group (MSG) of the MSi 102, that is, MSs that areclose to MSi 102, must inform the RS 106 whether one or more of the MSshave decoded the uplink packet from the MSi 102.

In one embodiment of the present invention, with reference to FIG. 1A,the RS performs network coding, without acknowledgement (ACK) feedbackmessages from MSs near the MSi 102 for the uplink packets transmitted bythe MSi 102. The downlink packet selection by the RS 106 is based onlyon an MSG report. For example, a downlink packet to the MSj 104 isselected. Therefore, by not transmitting ACK messages for any of theuplink packets received by the RS 106 from the MSi 102, no extra delaysare imposed on the transmission of the uplink packets. The BS canrecover the uplink packets from the network coded packets usingpreviously cached downlink packets. The downlink packet to MSj 104 canbe a delay tolerant packet, such that the RS 106 and the MSj 104 canperform additional operations to recover the downlink packet, if theuplink packet from MSi 102 has not been decoded by MSj 104.

In FIG. 1A, for example, the MSj 104 can be configured to provide a twostate or three state feedback for a network-coded packet from RS 106.The two state feedback can include, for example, an ACK message or a notacknowledged (NAK) message. The three state feedback can include, forexample, an ACK message, a NAK message for a failed uplink packet and aNAK message for a failed downlink packet.

Therefore, by not transmitting ACK messages for any of the uplinkpackets received by the RS 106, no extra delays are imposed on thetransmission of the uplink packets. Furthermore, control channeloverhead can be reduced since only scheduled downlink MSs that arereceiving downlink packets from network-coded transmissions from RS 106provide feedback. Since downlink-heavy MSs receive data instead oftransmitting data during the majority of time, a lower burden is imposedon the battery of the MSs. In addition, opportunities for receiving anddecoding more uplink packets by the MSs can be increased to create agreater potential for network coding. However, even if a downlink packetis delay tolerant, the RS 106 should still choose an appropriatedownlink packet for performing network coding with an uplink packet inorder to avoid losing the advantage provided by network coding.

In one embodiment of the invention, the MSj 104 in FIG. 1A can recoverfrom a failed network coded transmission by utilizing at least onepreviously received transmission.

For example, if the MSj 104 fails to decode an uplink packet “x”transmitted by the MSi 102 before receiving a network coded packet “y,”where the uplink packet x is needed to recover information from thenetwork coded packet y, there may be other opportunities for the MSj 104to recover the uplink packet x after the network coded packet y isreceived. Such opportunities may include reception by the MSj 104 of ahybrid automatic repeat request (HARQ) retransmission of the uplinkpacket x from the RS 106 to the BS 108, reception by the MSj 104 of aHARQ retransmission of the uplink packet x from the RS 106 to the MSj104, or reception by the MSj 104 of a transmission from the RS 106 of anetwork coded packet generated by either network coding the HARQretransmission of the uplink packet x with an uplink packet from the MSj104, network coding the HARQ retransmission of the uplink packet x witha HARQ retransmission of an uplink packet of an MSk (not shown in FIG.1A) in the network 100 which was previously decoded and stored by theMSj 104, network coding the HARQ retransmission of uplink packet x witha downlink HARQ retransmission to the MSk which was previously decodedand stored by the MSj 104, network coding the HARQ retransmission of theuplink packet x with forward link (FL) control channel blocks, or othernetwork coding combinations described below.

In one embodiment, the MSj 104 stores any received yet undecoded samplesof network coded packets, such as the network coded packet y, or uplinkpackets, such as the uplink packet x, for combining with any laterreceived retransmissions of the uplink packet x, for decoding the uplinkpacket x, and for using x to recover the downlink packet to MSj 104 fromthe network coded packet y.

FIG. 2 illustrates failed downlink packets and failed bi-directionalnetwork coded packets in accordance with one embodiment of the presentinvention. As will be described below, the RS 106 can send onetransmission following multiple failed transmissions for correcting themultiple failed transmissions. For example, in the followingdescriptions, a network coded packet that includes a packet A and apacket B is formed by a transmitter by network coding HARQretransmissions of the packet A and the packet B.

In FIG. 2, the RS receives uplink packets from various MSs, such as MS1,MS2, MS3 and MS4 and transmits downlink packets or network codedpackets, where the network coded packets include downlink packets andthe received uplink packets. For example, with reference to FIG. 2, MS1has failed to receive the uplink packet “UL1” from MS4 and, therefore,MS1 cannot recover the downlink packet “DL1” included in the networkcoded packet “NC1.” However, after being informed by MS1 that MS1 didnot decode UL1 needed to recover DL1, the RS can transmit either anothernetwork coded packet including UL1 and uplink packet “UL2” that hasalready been decoded by MS1, a network coded packet including UL1 andnetwork coded packet “NC3” that has already been decoded by MS1, or anetwork coded packet including UL1 and downlink packet “DL3” that hasalready been decoded by MS1. Similarly, if the MS1 has failed to decodepacket “DL4”, the RS can transmit a network coded packet including DL3that has already been decoded by the MS1 and downlink packet “DL4,” or anetwork coded packet including DL4 and UL2 that has already been decodedby MS1.

Therefore, the RS 106 can send one transmission, such as a network codedmessage, which can be used by both MS1 and MS3 to recover data inpreviously failed transmissions. For example, if the RS transmits anetwork coded message including DL3 that has already been decoded by MS1and including DL4 that has already been decoded by MS3, MS1 can use thealready decoded DL3 to recover DL4 from the network coded message andMS3 can use the already decoded DL4 to recover DL3 from the networkcoded message.

For example, instead of retransmitting the downlink packet DL1 after afailed transmission of the network coded packet NC1, a network codedtransmission as described above can be utilized. A network coding gaincan be realized since each one of the transmitted coded bits in anetwork coded packet can be recoded to carry at least two coded bits.The network coding can be performed outside of the bidirectional zone.MS1 can recover additional coded samples of packet UL1 from thenetwork-coded transmission. Such recoded packets can be smaller in sizein relation to a new transmission of the downlink packet DL1 or DL4because MS1 can utilize the previously failed reception of packet UL1and combine it with additional coded samples of packet UL1 from thenetwork-coded transmission.

In one embodiment of the invention, an MS attempting to decode bothuplink packets from and downlink packets to other MSs may store thedecoded information. The MS may also attempt to decode and storedownlink packets intended for other MSs after extracting coded downlinkpackets from network coded transmissions, if the MS has stored therequired information for such extraction, such as an uplink packet usedto generate the network coded packet.

In one embodiment, if a timer is associated with one or more of thedecoded and stored packets, a decoded and stored packet can be deletedupon the expiration of the timer.

To generate a desirable network-coded transmission discussed above, theRS needs to determine the information needed by MS1 that has beencorrectly received by MS3, and the information needed by MS3 that hasbeen correctly received by MS1. Therefore, feedbacks from MS1 and MS3are needed.

In one embodiment, two types of FL control channels, such as type “A”ACK channel assignments and type “B” ACK channel assignments, can beused to perform the procedures described above.

An example of the abovementioned feedbacks will now be discussed. MS1through MS(k−1) can each fail to receive either DL packets orbi-directional network coded packets from RS, before the MSk hasreceived a packet z. The packet z can be either a DL packet or abi-directional network coded packet intended for MSk. If MSk fails toreceive the packet z, MSk then communicates back to the RS and indicateswhether it has information regarding the packets that MS1 throughMS(k−1) failed to receive. Such a communication back to the RS isreferred to as a type “A” ACK. For example, the type “A” ACK from theMSk discussed above can indicate whether the MSk has decoded the DLpacket or the UL packet contained in the network coded bi-directionalpacket.

Assuming MSk has information that can be used by MS1, MS3 and MS5, theRS allocates one ACK channel for each of MS1, MS3 and MS5 that can beused to communicate back to the RS to indicate whether any of MS1, MS3or MS5 has information useful to MSk. Such communication back to the RSis referred to as a type “B” ACK. Based on the type “B” ACKs from theMS1, MS3 and MS5, the RS can generate a network-coded transmissionbeneficial to, for example, MSk and MS1. For example, the type “A” andtype “B” ACKs discussed herein can be configured to use on-off keying,such that the transmitter of the ACK channel only signals when there isa positive acknowledgement.

In one embodiment, after the intended receiver, such as MS, receives abi-directional network coded packet or a downlink packet “p” from a BSor RS, the MS can feed back additional information if requested byeither the BS or RS and if the decoding fails. Feedback assignmenttechniques are discussed below. The additional information (type “A”ACK) can be, for example, a set “S0” of IDs of any of the stored packetsthat is either a downlink packet or an uplink packet associated with anetwork coded packet, and which has not been reported. The resource oftype “A” ACK can be allocated at a later slot or sub-frame than the timeof the 2 or 3 state ACK for the packet p, such that the network canreallocate the resources for the type “A” ACK for other uses if thepacket p is positively acknowledged by the MS,

In one embodiment of the invention, the BS or RS echoes an ACK/NAKmessage transmission according to the previously described two state orthree state feedback. If a NAK message is transmitted, a set “S1” andACK channel assignments associated with each member in the set S1 arealso sent by the BS or RS. The set S1 represents all packet IDs storedby the MS known to the BS or RS and which is a downlink packet or anuplink packet associated with a network coded packet.

If an ACK message is echoed, then other MSs delete the decoded packet pif the packet p is a downlink packet and delete any stored uplink ordownlink packets used to generate the packet p if the packet p is abi-directional network coded packet.

If a NAK for a downlink packet message is echoed, that is, the intendedreceiver has decoded the uplink packet contained in the bi-directionalnetwork coded packet, then the other MSs delete any stored uplinkpackets used to generate the packet p if the packet p is abi-directional network coded packet.

In one embodiment of the invention, other MSs transmit an ACK messagefor the packet p based on the type of the NAK echoed by BS or RS and theACK channel assignment.

For example, if the BS or RS echoes an ACK message to a packet p and anMS is in the set S1, then the MS having an assigned ACK resourcetransmits a type “B” ACK if it has decoded the packet p in accordancewith an on-off keying technique. If the BS or RS echoes an uplink packetNAK and the MS is in the set S1, then the MS ACKs if it has decoded allof one or more uplink packets used to generate the packet p if thepacket p is a bi-directional network coded packet. If the BS or RSechoes a downlink packet NAK and the MS is in the set S1, then the MSACKs if it has decoded the downlink packet used to generate the packet pif the packet p is a bi-directional network coded packet. If the BS orRS echoes an ACK, then BS or RS does not allocate ACK channel resourcesfor a type “B” ACK.

In one embodiment, a feedback from an intended receiver MSk does notcontain the additional information, such as a type “A” feedback, and BSor RS does not allocate the ACK resource for a type “B” ACK, if thepacket p is successfully received by MSk.

The type “A” ACK channel assignments are additional assignments to thereceiver of a network coded packet or a downlink packet and are used forsignaling whether an MS has stored packets related to a failed networkcoded packet or a downlink packet of other MSs. For example, the set S1can be generated based on the type “A” ACKs.

In one embodiment, the type “B” ACK channel assignments are for otherMSs who have previously failed network coded packets or failed downlinkpackets and the receiver of a current network coded packet or downlinkpacket has indicated that it has stored packets related to their failedpackets. The failed network coded packets or failed downlink packets areassigned an ID. An exemplary timeline of type “A” and type “B” ACKs areshown in FIG. 3.

In one embodiment, the type “A” ACK assignment to the MSk can also beused as parity bits of previously failed transmissions to other MSs, andthe type “B” ACK assignment to the MSs in the set S1 can also be used asparity bits of the failed transmission to the MSk.

FIG. 4 illustrates a type “A” ACK assignment message 400 in accordancewith one embodiment of the present invention. The type “A” ACKassignment message 400 includes an ID field 402 for indicating the ID ofa packet “p” transmitted in the current or a previous sub-frame, a flagfield 404 for indicating whether the receiver of the packet p is also areceiver of the downlink packet at the current slot or sub-frame (SF),and bitmap bits 410 that are exclusive OR-ed (XOR-ed) with thecorresponding packet p parity bits 408. Depending on the type of echoedACK/NAK associated with packet p, packet p parity bits 408 can also bethe parity bits of the uplink packet which was used to generate anetwork coded packet p.

In FIG. 4. the bitmap bit “Bx” can indicate whether a type “A” ACKchannel is assigned to the downlink packet receiver whose physicaldownlink control channel (PDCCH) block is at position “x” in the currentSF. Assuming a pre-configured starting position of ACK channelsassociated with a packet ID, the ACK channel position of x is known fromthe bitmap.

In one embodiment, if a minimum assignment rule is satisfied for bitposition x, the BS or RS must set the bit Bx to “1” to assign an ACKchannel. For example, the network coded packet ID p has an uplink packetNAK and is generated using an uplink packet transmitted from an Mi andthe PDCCH receiver at position x is or was in the MSG of the MS.

If a minimum non-assignment rule is satisfied for bit position x, the BSor RS must set the bit Bx to “0” to not assign an ACK channel. Forexample, the downlink packet ID p has a less robust MCS than the MCSassigned to the PDCCH receiver at position x.

The BS or RS is free to set the bit value of the bitmap if none of theminimum criteria are satisfied.

When a type “A” ACK assignment is received at the PDCCH receiver, if anMS at bit position x has stored information related to the packet p,then the MS can correctly find its ACK channel position. One suchexemplary scenario can occur when an MS has a stored uplink packet whichwas used to generate a network coded packet p and the network codedpacket p has an uplink NAK. Otherwise, the MS ignores the assignment inaccordance with an on-off keying technique.

When a type “A” ACK assignment is received at the receiver of a packetp, the receiver of the packet p can take additional parity bits from thetype “A” ACK assignments if the MS at position x, that is, the PDCCHposition x, satisfies the minimum assignment or non-assignment rules.For example, if the MS satisfies the non-assignment rule, the receiverof the packet p can take the bit value “0”, which is then XOR-ed withthe value of bit x Bx. The result of the XOR operation is an additionalparity bit for the packet p. The receiver of packet p ignores parity bitx from the type “A” ACK assignments if the MS at bit position x, thatis, the PDCCH position x, satisfies neither the minimum assignment nornon-assignment rules.

FIG. 5 illustrates a network 500 in which an exemplary type “A” ACKchannel assignment is performed in accordance with one embodiment of thepresent invention. Network 500 includes BS 501, MS1 512, MS2 514 and MS3516.

In FIG. 5, the BS 501 initially transmits a downlink packet p intendedfor the MS3 516. The MS3 516, however, fails to decode the packet p. TheMS1 512 stores information related to the packet p, however, the MS2 514does not store information related to the packet p. At the currentsub-frame, downlink packets to MS1 and MS2 are scheduled, and controlinformation, such as type “A” ACK channel assignments are alsoscheduled. The BS 501 transmits the control information including astarting position and a bitmap XOR-ed with retransmitted data, that is,parity bits, of packet p. The MS1 512 uses the stored informationrelated to the packet p and the control information by the BS 501 toacquire an ACK channel position and ACK. The MS2 514, not having storedinformation related to the packet p, does not know the packet p andignores the channel assignment. The MS3 516 receives the packet p andacquires parity bits if some of the PDCCH receivers satisfy the minimumrules. Therefore, the assigned ACK channel performs on-off keying.

FIG. 6 illustrates a type “B” ACK assignment message 600 in accordancewith one embodiment of the present invention. As shown in FIG. 6, thetype “B” ACK assignment message 600 includes bitmap bits 618 that areXOR-ed with packet q parity bits 620. Each bit position of the bitmap618 corresponds to a previously transmitted packet by the BS or RS. Thebitmap bit Bx of the bitmap bits 618 indicates whether a type “B” ACKchannel is assigned to the receiver of the packet with ID x, that is,whether the packet ID x is in the set S1. Assuming a preconfiguredstarting position associated with a packet ID, the ACK channel positionof x is known from the bitmap 618. Packet q parity bits 620 are theparity bits of the currently failed transmission to the MS.

FIG. 7 illustrates a network 700 in which an exemplary type “B” ACKchannel assignment is performed in accordance with one embodiment of thepresent invention. Network 700 includes BS 701, MS1 722, MS2 724 and MS3726.

In FIG. 7, the BS 701 transmits data in the network 700 to MS3 726. TheMS1 722 stores the data from the BS 701, however, the MS2 724 does notstore the data. The BS 701 also transmits control information includinga starting position and a list or bitmap indicating set “S1” that isXOR-ed with a retransmission of the data intended for the MS3 726. TheMS1 722 uses the stored data and the control information by the BS 701to acquire an ACK channel position and ACK. The MS2 724, not havingstored the data, does not know the retransmitted data and ignores thechannel assignment. The MS3 726 knows S1 and can acquire theretransmitted data, that is, additional parity bits of the data, in thecontrol information. Therefore, the assigned ACK channel performs on-offkeying.

FIG. 8 illustrates a network 800 in which an exemplary ACK/NAK echo fora bi-directional network packet p to MS3 832 is performed in accordancewith one embodiment of the present invention. Network 800 includes BS801, MS1 828, MS2 830 and MS3 832.

In FIG. 8, the BS 801 transmits a two-bit network coded control message(bit 1, bit 0), which can be transmitted together with the type “B” ACKchannel assignment described above, where bit 0 represents an uplinkparity bit that is XOR-ed with an echoed uplink ACK and where bit 1represents a downlink parity bit that is XOR-ed with an echoed downlinkACK. The MS1 828, which had overheard the uplink packet in the networkcoded packet, recovers ACK bit 0 using the uplink packet and transmits atype “B” ACK if the recovered ACK bit 0 indicates a NAK. The MS1 828discards the stored uplink packet in the network coded packet p if therecovered ACK bit 0 indicates an ACK. The MS2 830, which had overheardthe network coded packet p and the uplink packet in the network codedpacket p, recovers the downlink packet from the network coded packet pusing the uplink packet. The MS2 830 uses the downlink packet and theuplink packet to recover ACK bit 0 and bit 1 and transmits a type “B”ACK if any of the recovered ACK bits indicates a NAK. The MS2 830discards the stored packet corresponding to the recovered ACK bit if therecovered ACK bit indicates an ACK. The MS3 832 knows the echoed uplinkACK and the echoed downlink ACK and acquires the uplink and downlinkparity bits, that is, additional parity bits.

FIG. 9 illustrates a network 900 in which an exemplary ACK/NAK echo fora downlink packet p to MS3 938 is performed in accordance with oneembodiment of the present invention. Network 900 includes BS 901, MS1934, MS2 936 and MS3 938.

In FIG. 9, the BS 901 initially transmits a downlink packet p andsubsequently transmits a control message with a single network coded bit(bit 0), which can be transmitted with a type “B” ACK, where bit 0represents a downlink parity bit that is XOR-ed with an echoed downlinkACK. The MS1 934 having overheard and decoded the downlink packet fromthe BS 901, recovers the ACK bit from the single network coded bit andtransmits a type “B” ACK if the recovered ACK bit indicates a NAK. TheMS2 936 did not decode the downlink packet from the BS 901 and doesnothing. The MS3 938 knows the echoed downlink ACK and acquires thedownlink parity bit, that is, an additional parity bit that can be usedfor decoding downlink packet p.

The forward link overhead is effectively reduced by the disclosedembodiments because the control messages for ACK channel assignments andechoes can also be used for transmitting additional parity bits of thefailed packets.

FIGS. 10A through 10C illustrate a network 110 that uses network codedcontrol information for identifying a downlink receiver that willbenefit from network coding in accordance with one embodiment of thepresent invention.

As shown in FIGS. 10A through 10C, the network 110 includes the MS 1040,the first receiver 1042, the second receiver 1044 and the BS 1046. Thefirst receiver 1042 and the second receiver 1044 can each be, forexample, a user equipment.

As shown in FIG. 10A, the BS 1046 transmits the 1st message 1048 to thefirst receiver 1042 and the 2nd message 1052 to the second receiver1044. The MS 1040 decodes both the 1st message 1048 and the 2nd message1052. The first receiver 1042 transmits a HARQ NAK message 1050 to theBS 1046, and the second receiver 1044 transmits a HARQ ACK message 1054to the BS 1046.

Thereafter, as shown in FIG. 10B, the MS 1040 transmits an uplinkmessage 1056 to the BS 1046. The first receiver 1042 and the secondreceiver 1044 overhear and decode the UL message 1056. The BS 1046,which failed to decode the UL message 1056, transmits a HARQ NAK messageto the MS 1040.

As shown in FIG. 10C, the BS 1046 then transmits control information1062 to the MS 1040. The MS 1040 can use the control information todetermine which of the previously received 1st message 1048 or thepreviously received 2nd message 1052 should be network coded with theretransmission of its UL message 1056. For example, with reference toFIG. 11, the control information 1062 can be a two-bit binary messagewhere the first bit is generated by network coding (“nc”), for example,by performing an XOR operation on, a portion of the information or aparity bit in the 1st message 1048 and information indicating whetherthe first receiver needs help, and where the second bit is generated bynetwork coding a portion of the information or a parity bit in the 2ndmessage 1052 and information indicating whether the second receiverneeds help. For example, the portion of the information in the 1st or2nd messages 1048 and 1052 can be a single binary value, such as “0” or“1.”

Therefore, with reference to FIG. 10C, since the first receiver 1042failed to receive the 1st message 1048 and needs assistance, the controlinformation 1062 can indicate to the MS 1040 that the MS 1040 shouldnetwork code its retransmission of the uplink message 1056 with the 1stmessage 1048. The MS 1040 can then transmit the network coded message,such as the network coded message 1060, to the BS 1046 and firstreceiver 1042. Since the first receiver 1042 previously overheard andknows the uplink message 1056 used to generate the network coded message1060, the first receiver 1042 can use the uplink message 1056 to recoverthe 1st message 1048 from the network coded message 1060.

It should be noted that the first receiver 1042 receives one or moreadditional parity bits from the control information 1062. Moreover, itshould also be noted that the receiver which has failed to receive amessage, such as the first receiver 1042, receives additional assistancefrom the control information 1062 regardless of whether the MS 1040 hasoverheard the message that the receiver failed to receive.

FIGS. 12A through 12C illustrate a network 120 that uses network codedcontrol information for ACK channel assignment in accordance with oneembodiment of the present invention. As shown in FIGS. 12A through 12C,the network 120 includes the MS1 1266, the MS2 1268, the MS3 1270, thefirst transmitter 1272, the first receiver 1274, and the RS 1276. Forexample, the first transmitter 1272 can be an MS and the first receiver1274 can be a BS.

In FIG. 12A, the RS 1276 has buffered a downlink message to the MS31270. As shown in FIG. 12A, the first transmitter 1272 transmits a 1stmessage 1279, which can be an uplink message, to the RS 1276. The MS11266 overhears and decodes the 1st message 1279. As also shown in FIG.12A, the first receiver 1274 transmits a 2nd message 1280 intended forthe MS1 1266, which is received by the RS 1276.

Thereafter, with reference to FIG. 12B, the RS 1276 transmits controlinformation 1278. For example, with reference to FIG. 13, the controlinformation 1278 can be a three-bit binary message where the first bitis generated by network coding (herein also referred to as “nc”), forexample, by performing an XOR operation on, a portion of the informationor a first parity bit in the 1st message 1279 and information thatindicates the ACK channel assignment for MS1 1266 for indicating whetherthe 1st message 1279 was received by MS1 1266, where the second bit isgenerated by network coding a portion of the information or a secondparity bit in the 1st message 1279 and information that indicates theACK channel assignment for the MS2 1268 for indicating whether the 1stmessage 1279 was received by MS2 1268, and where the third bit isgenerated by network coding a portion of the information or a thirdparity bit in the 1st message 1279 and information that indicates theACK channel assignment for the MS3 1270 for indicating whether the 1stmessage 1279 was received by MS3 1270. For example, the portion of theinformation in the 1st messages 1279 can be a single binary value, suchas “0” or “1.”

Each of the ACK channel assignments discussed above with respect to MS11266, MS2 1268, and MS3 1270 is based on whether the RS 1276 hasbuffered a downlink packet transmitted by the BS 1274 to an MS. Forexample, if the RS 1276 has not buffered a downlink packet transmittedby the BS 1274 to the MS2 1268, the MS2 1268 does not need to indicatewhether it has overheard the 1st message 1279 because the RS 1276 wouldnot be able to subsequently generate a bi-directional network-codedmessage using the 1st message 1279 and the downlink packet transmittedto the MS2 1268.

Therefore, with reference to FIG. 12B, since the MS1 1266 overheard the1st message 1279, the MS1 1266 can acquire the ACK channel assignmentfor the 1st message 1279 from the control information 1278. The MS21266, which also overheard the 1st message 1279, knows no ACK channelassignment for the 1st message 1279 from the control information 1278.In other words, there is no downlink data from the BS/first receiver1274. The MS3 1270 did not overhear the 1st message 1279 and, therefore,ignores the ACK channel assignment. In addition, the BS 1274 hasknowledge of the MSs, such as the MS1 1266 and the MS3 170, for which ithas forwarded downlink packets to the RS 1276. Therefore, based on theknowledge of the MSs and the control information 1278, the BS 1274 canrecover a portion of the information or parity bits in the 1st message1279, which will be forwarded by the RS 1276 in the near future.

With reference to FIG. 12C, the MS1 1266 transmits an ACK message 1286for the 1st message 1279 to the RS 1276. The MS3 1270 does not transmitany messages because it has not received 1st message 1279, which isinterpreted by the RS 1276 as a NAK because the ACK channel is on-offkeying. Based on the received ACK, the RS 1276 knows that the buffereddownlink message to the MS1 1266 should be network coded with the 1stmessage 1279, and the RS 1276 generates and transmits the network codedmessage 1282 including the 1st message 1279 and the 2nd message 1280.Since the MS1 1266 previously overheard and knows the 1st message 1279that was used to generate the network coded message 1282, the MS1 1266can use the 1st message 1279 to recover the 2nd message 1280 from thenetwork coded message 1282. Similarly, if the recovered 1st message 1279at the BS 1274 cannot be decoded, the recovered 1st message 1279 can becombined with the portion of the information or parity bits in the 1stmessage 1279 recovered from the control information 1278.

FIG. 14 is a flowchart illustrating a method performed by a BS inaccordance with one embodiment of the invention. With reference to FIG.14, the BS receives a signal containing a transmitted first signalincluding a network coded message and a transmitted second signalincluding a non-network coded message, where the second signal istransmitted according to at least one transmission parameter (S1401).The BS receives the at least one transmission parameter (S1403) and thendetermines an interference to the transmitted first signal caused by thetransmitted second signal, where the interference is determined usingthe at least one transmission parameter (S1405). The BS then removes thedetermined interference from the signal to recover the transmitted firstsignal (S1407).

FIG. 15 is a flowchart illustrating a method performed by a UE or NE inaccordance with one embodiment of the invention. With reference to FIG.15, the UE or NE receives a bitmap including at least a first bit thatis a result of an exclusive OR operation between a portion of the firstmessage and first data which can facilitate determining information thatshould be network coded with the first message in a future transmission,where the UE is either a transmitter or a receiver of the futuretransmission, where a first receiver for the bitmap is required toreceive the first message and has implicit or explicit knowledge of thefirst data, and where a second receiver for the bitmap has implicit orexplicit knowledge of the first message and is required to receive thefirst data (S1509).

The UE determines the first data from the first bit in the bitmap usingthe first message when the UE is the transmitter of the futuretransmission (S1511). The UE identifies the first data associated withthe first message, where the first data indicates whether the firstreceiver successfully received the first message when the UE is thetransmitter of the future transmission (S1513). The UE generates anetwork coded message including a retransmitted UL message and the firstmessage when the UE is the transmitter of the future transmission andwhen the first receiver has not successfully received the first message(S1515). The UE then transmits the network coded message (S1517).

FIG. 16 shows a block diagram of an MS 1600 in accordance with oneembodiment of the present invention. The MSs described herein, which arealso herein referred to as “user equipments” (UEs), can be configuredaccording to the exemplary MS 1600 discussed below.

The MS 1600 includes a microprocessor (or digital signal processor)1684, RF module 1686, power management module 1688, antenna 1690,battery 1692, display 1694, keypad 1696, memory 1695, speaker 1697 andmicrophone 1698.

A user enters instructional information, such as a telephone number, forexample, by pushing the buttons of a keypad 1696 or by voice activationusing the microphone 1698. The microprocessor 1684 receives andprocesses the instructional information to perform the appropriatefunction, such as to dial the telephone number. Operational data may beretrieved from the memory module 1695 to perform the function.Furthermore, the microprocessor 1684 may display the instructional andoperational information on the display 1694 for the user's reference andconvenience.

The microprocessor 1684 issues instructional information to the RFmodule 1686, to initiate communication, for example, transmits radiosignals including voice communication data. The RF module 1686 includesa receiver and a transmitter to receive and transmit radio signals. Anantenna 1690 facilitates the transmission and reception of radiosignals. Upon receiving radio signals, the RF module 1686 may forwardand convert the signals to baseband frequency for processing by themicroprocessor 1684. The processed signals would be transformed intoaudible or readable information outputted via the speaker 1697, forexample. The microprocessor 1684 also includes the protocols andfunctions necessary to perform the various processes described herein.

It will be apparent to one skilled in the art that the MS 1600 may bereadily implemented using, for example, the microprocessor 1684 or otherdata or digital processing device, either alone or in combination withexternal support logic. Although the present invention is described inthe context of mobile communication, the present invention may also beused in any wireless communication systems using mobile devices, such asPDAs and laptop computers equipped with wireless communicationcapabilities. Moreover, the use of certain terms to describe the presentinvention should not limit the scope of the present invention to certaintype of wireless communication system, such as UMTS.

It should be noted that the BSs and RSs described herein canalternatively be referred to as network equipment (NE).

The preferred embodiments may be implemented as a method, apparatus orarticle of manufacture using standard programming and/or engineeringtechniques to produce software, firmware, hardware, or any combinationthereof. The term “article of manufacture” as used herein refers to codeor logic implemented in hardware logic (e.g., an integrated circuitchip, Field Programmable Gate Array (FPGA), Application SpecificIntegrated Circuit (ASIC), etc.) or a computer readable medium (e.g.,magnetic storage medium (e.g., hard disk drives, floppy disks, tape,etc.), optical storage (CD-ROMs, optical disks, etc.), volatile andnon-volatile memory devices (e.g., EEPROMs, ROMs, PROMs, RAMs, DRAMs,SRAMs, firmware, programmable logic, etc.). Code in the computerreadable medium is accessed and executed by a microprocessor.

The code in which preferred embodiments are implemented may further beaccessible through a transmission media or from a file server over anetwork. In such cases, the article of manufacture in which the code isimplemented may comprise a transmission media, such as a networktransmission line, wireless transmission media, signals propagatingthrough space, radio waves, infrared signals, etc. Of course, thoseskilled in the art will recognize that many modifications may be made tothis configuration without departing from the scope of the presentinvention, and that the article of manufacture may comprise anyinformation bearing medium known in the art.

The logic implementation shown in the figures described specificoperations as occurring in a particular order. In alternativeimplementations, certain logic operations may be performed in adifferent order, modified or removed and still implement preferredembodiments of the present invention. Moreover, steps may be added tothe above described logic and still conform to implementations of theinvention.

The foregoing embodiments and advantages are merely exemplary and arenot to be construed as limiting the present invention. The presentteaching can be readily applied to other types of apparatuses. Thedescription of the present invention is intended to be illustrative, andnot to limit the scope of the claims. Many alternatives, modifications,and variations will be apparent to those skilled in the art. In theclaims, means-plus-function clauses are intended to cover the structuredescribed herein as performing the recited function and not onlystructural equivalents but also equivalent structures.

What is claimed is:
 1. A method performed by a user equipment (UE) ornetwork equipment (NE), the method comprising: receiving, at the UE orNE, a bitmap comprising at least a first bit that is a result of anexclusive OR operation between a portion of a first message and firstdata which can facilitate determining information that should be networkcoded with the first message in a future transmission, wherein the UE iseither a transmitter or a receiver of the future transmission, wherein afirst receiver for the bitmap is required to receive the first messageand has implicit or explicit knowledge of the first data, and wherein asecond receiver for the bitmap has implicit or explicit knowledge of thefirst message and is required to receive the first data.
 2. The methodof claim 1, wherein when the UE is the transmitter of the futuretransmission, the method further comprises: determining, by the UE, thefirst data from the first bit in the bitmap using the first message;identifying, by the UE, the first data associated with the firstmessage, wherein the first data indicates whether the first receiversuccessfully received the first message; generating, by the UE, anetwork coded message comprising a retransmitted uplink (UL) message andthe first message when the first receiver has not successfully receivedthe first message; and transmitting the network coded message.
 3. Themethod of claim 1, wherein the first receiver has previously received anuplink (UL) message, and wherein the first receiver determines the firstmessage from the network coded message using the UL message.
 4. Themethod of claim 1, wherein the first receiver recovers the portion ofthe first message from the first data in the bitmap.
 5. The method ofclaim 1, wherein when the UE is the receiver of the future transmission,the method further comprises: determining, by the UE, an acknowledgment(ACK) channel assignment using the first message, wherein the ACKchannel assignment is used to notify a network that the UE has receivedthe first message, wherein an acknowledgment or a non-acknowledgement onthe ACK channel is indicated using on-off keying; transmitting an ACKsignal to the network according to the ACK channel assignment; andreceiving, at the UE, the future transmission comprising a network codedmessage, wherein the network coded message comprises a second message tothe UE and the first message.
 6. The method of claim 5, wherein thesecond receiver has previously transmitted the first message to a relaystation, and wherein the UE determines the second message from thenetwork coded message using the first message that was overheard, andwherein the first receiver determines the first message from the networkcoded message using the second message which the first receiver haspreviously transmitted to the relay station.
 7. The method of claim 6,wherein the first receiver recovers the portion of the first messagefrom the bitmap using data indicating whether a previous transmissionfrom the first receiver occurred.
 8. The method of claim 5, wherein thenetwork generates the future transmission based on the ACK signalreceived by the network.
 9. The method of claim 6, wherein the firstreceiver is a base station (BS).
 10. The method of claim 7, wherein thefirst receiver is a base station (BS).
 11. A communication device,comprising: a radio frequency (RF) module; and a processor configured tocause the RF module to receive a bitmap comprising at least a first bitthat is a result of an exclusive OR operation between a portion of afirst message and first data which can facilitate determininginformation that should be network coded with the first message in afuture transmission, wherein the communication device is either atransmitter or a receiver of the future transmission, wherein a firstreceiver for the bitmap is required to receive the first message and hasimplicit or explicit knowledge of the first data, and wherein a secondreceiver for the bitmap has implicit or explicit knowledge of the firstmessage and is required to receive the first data.
 12. The communicationdevice of claim 11, wherein when the communication device is thetransmitter of the future transmission, the processor is furtherconfigured to: determine the first data from the first bit in the bitmapusing the first message; identify the first data associated with thefirst message, wherein the first data indicates whether the firstreceiver successfully received the first message; generate a networkcoded message comprising a retransmitted uplink (UL) message and thefirst message when the first receiver has not successfully received thefirst message; and cause the RF module to transmit the network codedmessage.
 13. The communication device of claim 11, wherein the firstreceiver has previously received an uplink (UL) message, and wherein thefirst receiver determines the first message from the network codedmessage using the UL message.
 14. The communication device of claim 11,wherein the first receiver recovers the portion of the first messagefrom the first data in the bitmap.
 15. The communication device of claim11, wherein when the communication device is the receiver of the futuretransmission, the processor is further configured to: determine anacknowledgment (ACK) channel assignment using the first message, whereinthe ACK channel assignment is used to notify a network that thecommunication device has received the first message, wherein anacknowledgment or a non-acknowledgement on the ACK channel is indicatedusing on-off keying; cause the RF module to transmit an ACK signal tothe network according to the ACK channel assignment; and cause the RFmodule to receive the future transmission comprising a network codedmessage, wherein the network coded message comprises a second message tothe communication device and the first message.
 16. The communicationdevice of claim 15, wherein the second receiver has previouslytransmitted the first message to a relay station, and wherein theprocessor is further configured to determine the second message from thenetwork coded message using the first message that was overheard, andwherein the first receiver determines the first message from the networkcoded message using the second message which the first receiver haspreviously transmitted to the relay station.
 17. The communicationdevice of claim 16, wherein the first receiver recovers the portion ofthe first message from the bitmap using data indicating whether aprevious transmission from the first receiver occurred.
 18. Thecommunication device of claim 15, wherein the network generates thefuture transmission based on the ACK signal received by the network. 19.The communication device of claim 16, wherein the first receiver is abase station (BS).
 20. The communication device of claim 17, wherein thefirst receiver is a base station (BS).